Conventionally, monitoring of uplift of a lava dome is mostly dependent on sense of an observer who is monitoring a camera image. A snapshot image of the camera image which is obtained by manual operation at an irregular interval is preserved by printing or the like. When images need to be compared, it is required to find a slight difference between the images by naked eyes. In addition, when a lava dome and a mountain ridge are detected from images, image changes are misidentified due to changes caused by the intensity of sunlight or changes in the luminance depending on time zones, weather, and seasons.
As for a conventional technique, Japanese Patent Application Publication No. 2003-139532 discloses a method including: measuring a latitude, a longitude, and an altitude of an imaging position; obtaining at the imaging position a picture image including an imaging target region, a specific point of the imaging target region, and a skyline; obtaining a picture image skyline from the picture image; obtaining a skyline on a map showing the imaging target from the imaging position by using known terrain elevation data; obtaining a coordinate transformation formula by matching the picture image skyline with the skyline on the map; and converting a picture image taken at the imaging position into a map (orthographic image) viewed from above in a vertical direction by using the coordinate transformation formula.
As for another conventional technique, Japanese Patent Registration No. 4220140 discloses an apparatus including a TV camera configured to monitor a mountain shape and an image processing unit configured to perform predetermined image processing based on a video signal from the TV camera. The image processing unit measures the amount of planar changes of the countour of the mountain shape before and after the change of the mountain shape by using the video signal from the TV camera, and map information having a GIS function is stored in a storage unit. A three-dimensional collapse amount is measured by overlapping images obtained by the TV camera on a digital map stored in the storage unit.
Conventionally, live image monitoring and image preservation using cameras have been performed to detect signs of natural disasters such as volcanic eruption, rock collapse, flooding of rivers and the like. However, there is no system having a function capable of easily comparing images of the same view angle stored at a regular interval.